The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. Venturi masks are used in the medical administration of oxygen. Venturi tubes, also termed “venturis”, are used to measure the speed of a fluid, by measuring pressure changes at different segments of the device. When fluid flows though a Venturi the pressure in the two ends of the tube will differ, directing the fluid to the “low pressure” portion of the tube. The amount of motion can be calibrated to the speed of the fluid flow.
According to Wikipedia, “spirometry (meaning the measuring of breath) is the most common of the Pulmonary Function Tests (PFTs), measuring lung function, specifically the measurement of the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.
“Most spirometers display the following graphs, called spirograms:                a volume-time curve, showing volume (liters) along the Y-axis and time (seconds) along the X-axis        a flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis        
“Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible. It is sometimes directly followed by a rapid inhalation (inspiration), in particular when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation.”
Wikipedia explains that the following results are often generated in spirometric tests:
Results often generated in spirometric testsAbbreviationNameDescriptionFVCForced Vitaltotal amount of air that can forcibly beCapacityblown out after full inspiration, measured inliters.FEV1Forcedamount of air that subject can forcibly blowExpiratoryout in one second, measured in liters. AlongVolume in 1with FVC it is considered one of theSecondprimary indicators of lung function.FEV1/FVCFEV1%ratio of FEV1 to FVC. In healthy adults thisshould be approximately 75-80%.PEFPeakspeed of the air moving out of your lungs atExpiratorythe beginning of the expiration, measured inFlowliters per second.FEFForcedaverage flow (or speed) of air coming out of25-75% orExpiratorythe lung during the middle portion of the25-50%Flowexpiration (also sometimes referred to as the25-75% orMMEF, for maximal mid-expiratory flow).25-50%FIFForcedsimilar to FEF 25-75% or 25-50% except25-75% orInspiratorythe measurement is taken during inspiration.25-50%Flow25-75% or25-50%FETForcedmeasures the length of the expiration inExpiratoryseconds.TimeSVCSlow VitalMaximum volume of air that can be exhaledCapacityslowly after slow maximum inhalation.TVTidal volumeDuring the respiratory cycle, a specificvolume of air is drawn into and then expiredout of the lungs. This volume is tidalvolume.MVVMaximumA measure of the maximum amount of airVoluntaryVoluntary that can be inhaled and exhaled in Ventilationone minute, measured in liters/minute.
Spirometry requires patient cooperation hence is normally repeated at least three times to ensure reproducibility. Certain spirometry results can be underestimated but never overestimated. Conventional technology pertaining to certain embodiments of the present invention is described in the following publications inter alia: U.S. Pat. No. 7,282,032 to Miller, U.S. Pat. No. 7,094,208 to Williams et al, and U.S. Pat. No. 7,063,669 to Brawner et al.
The disclosures of all publications and patent documents mentioned in the specification, and of the publications and patent documents cited therein directly or indirectly, are hereby incorporated by reference.